1. Field of the Invention
The present invention relates to drilling of wells, well fluids, and well fluid additives and to methods, apparatus and products related thereto.
2. Description of the Related Art
The purpose of a rotary oil rig is to drill a hole to a predetermined depth. And, hopefully, in the drilling process, passing to or through one or more oil and gas bearing reservoir rock formations. Since rigs are expensive to manufacture, they need to be movable. In addition, since the rock chips created by the drilling bit must be removed, mud is pumped through the drill pipe to the bit and back up the annulus or space between the drill pipe and the outer casing that is added as drilling proceeds. The mud is mixed, usually with water but sometimes with chemicals, in a chemical tank, then sucked from the mud pit and pumped via a standpipe and rotary hose to a swivel that is attached to a Kelly, which is itself attached to the drill pipe. The returning mud and rock chips that reach the surface move by gravity down a return line to a shale shaker designed to separate the returning mud from the shale for reuse. The remaining rock chips travel down a shale slide to a reserve pit.
Technology in drilling for oil and gas has for a number of years included horizontal or directional drilling. The horizontal drilling concept exposes more surface area of the producing zone than the conventional vertical drilling operations.
Horizontal drilling technology achieved commercial viability during the late 1980's. Its successful employment, particularly in the Bakken Shale of North Dakota and the Austin Chalk of Texas, has encouraged testing of it in many domestic geographic regions and geologic situations. Achievable horizontal bore hole length grew rapidly as familiarity with the technique increased; horizontal displacements have now been extended to over several miles. Some wells have featured multiple horizontal bores. Completion and production techniques have been modified for the horizontal environment, with more change required as the well radius decreases; the specific geologic environment and production history of the reservoir also determine the completion methods employed.
The technical objective of horizontal drilling is to expose significantly more reservoir rock to the well bore surface than can be achieved via drilling of a conventional vertical well. The desire to achieve this objective stems from the intended achievement of other, more important technical objectives that relate to specific physical characteristics of the target reservoir, and that provide economic benefits. Examples of these technical objectives are the need to intersect multiple fracture systems within a reservoir and the need to avoid unnecessarily premature water or gas intrusion that would interfere with oil production.
In both examples, an economic benefit of horizontal drilling success is increased productivity of the reservoir. In the latter example, prolongation of the reservoir's commercial life is also an economic benefit. Applications of horizontal drilling technology have included the drilling of fractured conventional reservoirs, fractured source rocks, stratigraphic traps, heterogeneous reservoirs, coalbeds (to produce their methane content), older fields (to boost their recovery factors), and fluid and heat injection wells intended to boost both production rates and recovery factors.
Horizontal drilling is the process of drilling and completing, for production, a well that begins as a vertical or inclined linear bore which extends from the surface to a subsurface location, just above the target oil or gas reservoir called the “kickoff point,” then bears off on an arc to intersect the reservoir at the “entry point,” and, thereafter, continues at a near-horizontal attitude tangent to the arc, to substantially or entirely remain within the reservoir until the desired bottom hole location is reached.
Most oil and gas reservoirs are much more extensive in their horizontal (areal) dimensions than in their vertical (thickness) dimension. By drilling that portion of a well that intersects such a reservoir parallel to its plane of more extensive dimension, horizontal drilling's immediate technical objective is achieved.
That objective is to expose significantly more reservoir rock to the wellbore surface than would be the case with a conventional vertical well penetrating the reservoir perpendicular to its plane of more extensive dimension. The desire to attain this immediate technical objective is almost always motivated by the intended achievement of more important objectives (such as avoidance of water production) related to specific physical characteristics of the target reservoir.
For example, if a producing zone is fifty feet in thickness and a vertical well is drilled through such a zone, then only fifty feet of the producing zone will be exposed for production. In contrast, a horizontally drilled well may penetrate the producing sand or zone by one thousand feet or more. The amount or volume of oil or gas production is directly proportional to the horizontal penetration in feet into the producing sand or zone. In horizontal or directional drilling where the drill pipe must bend in order to achieve the desired penetration into the producing zone, friction becomes a major problem. The primary source of friction is directly related to the adhesion of the drilling assembly to the wall cake which lines the drilled well bore. The capillary attractive forces generated by the adhesion of the drilling assembly to the wall cake are directly proportional to the amount or footage of the drilling assembly exposed to the surface of the wall cake.
In the drilling of horizontal wells, gauge problems, sticking of the drill string, reactive torque, hole erosion, and tortuosity between the dynamic work string and bore hole, are generally all exacerbated. Tortuosity includes the effect of rotation of the bit and its reactive torque against the formation thereby causing the bit, bottom hole assembly and drill string to buckle, turn and twist within the well bore. Tortuosity effects well path, penetration rate, pipe sticking, etc. In an effort to overcome these issues, many methods have been used in order to reduce friction between the drilling assembly and the wall cake.
One such method would be to add a liquid lubricant to the drilling fluid in order to reduce the coefficient of friction of the drilling fluid. These liquid lubricants include oils, such as hydrocarbon based oils, vegetable oils, glycols, etc. These liquid lubricants will usually reduce the coefficient of friction of the drilling fluid resulting in a reduction of friction between the drilling assembly and the wall cake of the well bore.
Another method has been the use of spherical drilling beads in the drilling fluid to function as the friction reducer. These drilling beads act like ball bearings and function as a lubricant in well drilling applications.
These spherical beads are generally selected to have specific gravity greater than that of the well fluid, such that due to the horizontal inclination of the borehole, gravity will segregate the spherical beads to a position “below” the drill string.
Drilling Sideways—A Review of Horizontal Well Technology and Its Domestic Application, April 1993, published by the Energy Information Administration, Office of Oil and Gas, of the U.S. Department of Energy, is an overview of horizontal drilling technology.
U.S. Pat. No. 5,839,520, issued Nov. 24, 1998, to Maillet, discloses a method of increasing the penetration rate of a drill string within a deviated well bore. The method includes providing a drill string with a drilling bottom hole assembly, and rotating the bit in order to create the deviated well bore as well as a filter cake on the walls of the well bore. A pill comprising a spherical bead is prepared and pumped down into the well bore. The pill is allowed to migrated to the low side of the bore hole so that tortuosity is reduced. A method of slide drilling, batch drilling, and running a liner in a well is also disclosed utilizing the spherical beads. In the novel methods disclosed, the spherical beads are allowed to migrate to the low side of the borehole and are allowed to penetrate through the borehole's filter cake.
IADC/SPE 72290, Drilling Fluids Design and Management for Extended Reach Drilling, C. Cameron, SPE, Halliburton Energy Services 2001, discloses use of solid glass beads for reduction in torque whilst running casing, which act as “ballbearings” between the casing or open hole and the drill pipe or casing.
U.S. Pat. No. 7,001,871, issued Feb. 21, 2006, to Rayborn, discloses water-based drilling fluid additive containing talc and graphite. The drilling fluid additive is provided wherein the additive is manufactured by a method comprised of admixing at least one carrier such as a polypropylene glycol to talc and subsequently admixing graphite to the talc and carrier mixture; and then admixing an uintaite (a natural black bitumen) to the talc, carrier and graphite mixture.
U.S. Patent Publication No. 20070111899, published May 17, 2007, to Wood, discloses pre-engineered pills for the improvement of drilling muds. By introducing pills of ground elastomer into the well, the pills can improve the lubricity of the mud as well as aiding in wellbore cleaning, prevention of bit balling and reduction of fluid loss to thief zones. The pills can be prepared either on site or at a remote location and then transported to the drilling site for use. When the pill is prepared on site, the ground elastomer and non-aqueous fluid should be in contact with each other for a period sufficient to insure that the non-aqueous fluid has impregnated the elastomer particles. This will typically run from about 15 to 30 minutes.